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  • Writer's pictureRaelyn Teague

Worldbuilding Moons |Worldbuilding 5|

Last time we learned about the different kinds of planets we can use to create a unique universe for our characters to live in, but I’ve got one post left in me about building your own solar system, so let’s wrap this up and learn about other celestial bodies in space!


Earth’s sole natural satellite is a tidally locked moon that scientists hypothesize was formed from debris left behind after a collision between Earth and a celestial body named Theia back when Earth was a youngin'.

Our moon—sometimes referred to by the names Luna, or, more rarely, Selene or Cynthia—has a fairly circular orbit around earth and is nearly spherical in shape. This round shape, as discussed in the last worldbuilding post, is because of the moon’s size. Small moons don’t have enough gravity to form into spheres and can come in all kinds of shapes, but the gravitational force of larger moons means they end up forming into spherical shapes.

Our moon is actually a rarity. Though other moons in the solar system are larger than ours, our moon is the largest natural satellite relative to the size of the planet it orbits. (Charon, one of Pluto’s moons, is larger still, but alas, Pluto got kicked out of the planet club). Its mass is a fair bit less than Earth’s, but its diameter is more than a quarter the size of Earth. That’s a pretty big ball to be flinging around space in our neighbourhood.

Some moons, especially the farther away from the sun they are, are made of ice, but our moon is rocky. Its surface has cracks, volcanic features, and craters—some of which are eternally cast in darkness and record temperatures colder than Pluto. Nowadays the moon is pretty lacking in the atmosphere department, but evidence shows that wasn’t always the case. However, it’s current lack of atmosphere, along with a lack of geological activity in recent millennia, is part of the reason the surface of the moon is slow to shift and change. This means that the surface of the moon looks today very much like it would have thousands of years ago, but maybe you want to create a moon with more active geology for your world. Maybe it has erupting volcanoes or even a weather system that means the appearance of your moon is ever shifting.

Though liquid water can’t long exist on the moon due to solar radiation, ice has been found on the moon’s surface. Which will be incredibly important should Earthlings ever want to sell off real estate on the moon or open up a lunar hotel. Shockingly, people need water to survive, and until we have major advances in space travel or can turn moon dust into Dasani, transporting water to the moon simply isn’t cost effective.

Given how brightly the moon can shine at night, it might surprise you to learn that the moon’s surface isn’t very reflective. One of the reasons it appears so bright in the night sky is simply because of how close the moon is to Earth. Imagine if you created a moon that was more reflective. Depending on how you arranged any lunar cycles for your world, the nights might be far brighter than ours. Maybe you’d risk blinding yourself by gazing up at the moon.

But let’s discuss those lunar phases, shall we? The phases of the moon are quite regular, which make them an excellent way to mark a calendar. Many calendars in use in our world are a mix of solar and lunar. You might want to consider how long it takes your moon to go around your planet. Will it make sense for the people in your world to base a calendar off the moon?

What about eclipses? On Earth, we’re able to witness a total solar eclipse now and then because even though our moon is far smaller than the sun, its closeness to Earth means it appears to be the same size. But what if you had a moon that appeared smaller? Well, it would never be able to fully block out the sun. I imagine this might have a slightly different cultural impact in your world than eclipses do here. There’s no shortage of stories set on Earth where people who don’t understand how an eclipse works think the world is coming to an end because the sun disappeared and cast the world in darkness. A moon too small to completely block out the sun wouldn’t be able to turn day to night, but it might be able to give the sun a kind of “Eye of Sauron” appearance. (But please don’t stare straight at an eclipse!) There could be interesting legends about this in your world’s history. If your people believe the sun is a deity, maybe a solar eclipse like this confirms to them that the sun god is watching them. Maybe this is why they think it isn’t safe to look at an eclipse—because daring to meet the sun god’s gaze results in the god punishing you. With temporary blindness and scalding retinas.

I would be remiss to end any discussion of the moon without talking about how its gravitational relationship with the earth affects the tides. (The sun also affects the tides, but not so greatly as the moon). The side of earth closest to the moon’s position, as well as the side of Earth directly opposite, bulge, creating high tides. This is true of Earth’s waters, but it may surprise you to learn it’s also true of Earth’s land. Luckily for us, the effect on the land isn’t noticeable to our weak, human senses, but perhaps you want to imagine a world where the moon’s gravitational effects have an even greater impact.

So that’s our moon in a nutshell, but what about your moon? Consider how many moons you want your world to have. If there are lots of them, do their gravitational pulls ever act on each other? Do they all have circular orbits, or do some of them have elliptical or horseshoe orbits? What are their lunar phases like? Are these moons rocky or icy? Do they have valuable minerals that are rare or absent from your world? Do any of these moons have their own atmosphere, and, perhaps most importantly to sci-fi and fantasy writers out there, could any of these moons support life?


Stars, planets, and moons aren’t the only things waiting in the vast universe. If you’re happy enough to simply have a planet with a sun and moon, you’re already good to go, but if you want to think about how other objects in space might impact your world, here are just a few of the things you might want to think about.


Asteroids are small bodies made of minerals or rock orbiting the sun that aren’t big enough to be considered planets but are larger than one metre in diameter. In case you were wondering, that leaves a lot of wiggle room, as the asteroid Ceres is nearly 1000 kilometre across. That’s one million times the minimum size requirement for those who are bad at math.

Asteroids can orbit the sun alone, they can orbit with a moon of their own, they can have a trojan relationship with a planet (as I mentioned in this post), or they can belong to an entire asteroid commune and travel around the sun in an asteroid belt. Our solar system has its own asteroid belt with millions of asteroids located between the orbits of Mars and Jupiter. But there are quite a few asteroids in our own neighbourhood too. There are nearly 1000 near-Earth asteroids that we know of, and that’s if we’re only counting the ones that are one kilometer in diameter or larger. To all of you out there who fear an apocalyptic event brought on by the collision of an asteroid with Earth, then, well, have fun with that knowledge. I’m sure it’s fine. It’s fine.

For the purposes of science fiction writers, asteroids may make for an interesting plot device, doomsday event, or even setting. Maybe your space pirates find themselves stranded after trying to escape the intergalactic navy by travelling through an asteroid belt but failing to soar through unscathed. Maybe you’re writing a survival story after an asteroid has collided with Earth and wiped out half the population. Or maybe your main character works on an asteroid mine, where they discover a rare mineral with unique, or deadly, properties.

Then there are meteoroids. Unlike asteroids, meteoroids are smaller and can be anywhere from a teensy little grain to one metre in diameter, and these little guys are constantly trying so, so hard to take Earth out. It’s estimated that 25 million of these guys and their pals enter our atmosphere every day. It happens so often we have names for the various stages of trying to kill us they go through. A meteoroid is one of these objects still in space. A meteor is a meteoroid (or comet or asteroid) that has entered Earth’s atmosphere and has been heated until it glows in a streak of light across the sky—your “shooting” or “falling” stars. Then a meteorite is whatever bit or piece of a meteor survived its fall to Earth.

Once I was out walking after dark and saw a meteor headed my way. “Cool,” I thought. “I like shooting stars!” But it actually got close enough I could hear it whistling through the air (which might not actually be that close at all, I have no idea) and see it breaking into smaller, flaming pieces as it headed my way. It probably landed in some farmer’s field ten kilometres away, but I remember having this moment of “Oh, shoot, did I almost die by meteor?” (Let’s be honest, that would be the way I’d leave this world.)

There aren’t any known deaths caused as a direct result of being hit by a meteor, but there is at least one recorded injury. In the 1950s, a woman in Alabama was struck after a meteor crashed through the roof of the house she was in and bounced off the radio.

Think about that during the next meteor shower.


A black hole is an object in spacetime with a gravitational field so strong that not even light can escape it. Anything that crosses the event horizon—that is the boundary between being able to escape the black hole and being unable to escape it—gets sucked in. Even information. This is known as the “black hole information loss paradox,” and it means that any parameters beyond mass, charge, and angular momentum (rotation) are lost once an object enters a black hole’s event horizon. It may not be that this information actually disappears, but rather that the information simply can’t be accessed—it can’t escape that event horizon. For now it makes it hard to study black holes except from at a distance.

Black holes can form when an object, such as a star, collapses in on itself, its internal pressure becoming too weak for its own gravitational pull. For a star, this might happen when it reaches the end of its life cycle and can no longer maintain the temperatures it once did. After it collapses, it sucks in mass within its reach. Sometimes it will draw in and absorb other stars, other black holes, and it may continue to grow in strength until it becomes a supermassive black hole. It’s believed that supermassive black holes form the centre of most galaxies, and the first photograph of a supermassive black hole was publicly released only in 2019.


You might think of comets as those big balls of fire in the sky that pass by the earth now and again, and you’d be, well, not entirely right.

The nucleus of a comet is an irregularly-shaped body made up of dust, rock, and ice, as well as frozen gasses. Comets remain frozen for much of their journey, but when they pass near enough to the sun, their ice releases dust and those gasses, which form what is called a “coma,” around the nucleus. The dust particles that make up the coma and tail of the comet will reflect sunlight, while the gasses will glow due to ionization, giving the comet their bright appearance. While the nucleus of a comet may only be between about 100 meters to as much as 60 kilometres across, the coma, may be thousands or millions of kilometres across, even larger than the sun.

You may think that the tail of a comet follows behind it as it zips along its way, but in fact comets actually have two tails. Comets do leave a tail of dust that arcs out behind them, known as a Type II tail, but their Type I tail is made up of gasses. These gas particles are more affected by solar radiation and solar wind, and so they will always point away from the sun. Larger debris the comet leaves in the path of Earth’s orbit may end up becoming a meteor shower once they collide with Earth’s atmosphere.

Comets can be according to the length of their orbit around the sun. “Short-period” comets have orbital periods of less than 200 years. “Long-period” comets can take 200 to thousands of years to orbit the sun and tend to have very eccentric orbits.

Though the idea is debated, some think that much of the water on Earth came from comets that collided with our fair planet. So for those of you who want to bring an alien species, a disease, or a new form of magic to your planet on the back of a comet, the idea isn’t entirely fantastical.

As a final note on comets, they don’t stick around forever. A comet that travels fast enough might leave its orbit and the solar system altogether. Comets that are made up of more fragile components may end up breaking apart. Of course comets can also collide with a planet or moon or shoot into the sun. But even if none of those things happen, comets fade. Long-period comets tend to fade faster, but eventually the parts of the comet that react to its passages close to the sun evaporate, leaving the comet as a simple lump of rock. Some of the asteroids near Earth are believed to be extinct comets.


This isn’t an object in space so much as a cool phenomenon I wanted to include because they were a pretty common but beautiful sight for me growing up. Auroras are a neat display of lights best seen the closer you are to either the north or south magnetic poles. They happen when solar wind causes disturbances in Earth’s magnetosphere. Electrically charged particles from the sun then collide with Earth’s atmosphere, making the particles glow. The colours seen in the sky are dependent on what gases the particles are colliding with. For example, greenish light comes from oxygen. But Earth isn’t the only place that experiences auroras. Most of the planets in our solar system get them, and so do some moons. Even comets can have them, and the world you build for your novel can have them too. Maybe your atmosphere has a different makeup than ours and colours that are rarer in auroras on Earth are just your basic variety aurora on your world.


When I first developed the world for Project: Noveljutsu, long before I started working on my Noveljutsu episodes, I didn’t put a ton of thought into how that world fit into its own solar system. I made an Earth-like planet with a slightly longer year, but it was otherwise just an Earth substitute.

Again, I feel the need to say that is okay. There’s nothing wrong with developing an Earth-like planet and moving on. That is allowed. That’s fine. It can even be argued that’s exactly what most writers should do. But I do find part of myself lamenting that I hadn’t considered what other neat things I might have done if I’d put more thought into my world.

But, as I have reminded you in other episodes, you don’t have to do all your planning for a novel—not even worldbuilding—before you write the book. So I’m going to fit in a little extra worldbuilding now.

I’ll speak on this more when we get to episodes about worldbuilding religion, but one of the major cultures in my world predominantly believe in a trinity of goddesses. Like other goddess triads, they can be arranged into the maiden, mother, and crone figures. I thought it would be great if there were three celestial bodies that might play into this culture’s beliefs about their goddesses. Because of other attributes I’ve given to these goddesses, the sun seems to best fit the mother goddess. A moon could fit both the maiden or the crone goddesses, so I’ve decided to add a second moon. The first moon will be a large, spherical moon to fit the maiden, and the second moon will me an irregularly-shaped, kinda gnarly-looking moon. While it’s much smaller than the first moon, it’s closer to the planet, so it appears only a little smaller. And this gnarly-looking moon can be associated with their crone goddess.


Your challenge for this episode is simply to go out and look at the stars. Hopefully you have access to a place where the stars are visible, if not simply go out and look at the night sky or find pictures in an image search. Just take some time to relax, think, and be inspired by the vastness of the universe around us. I think we often don’t take the time to do this, and it can be so inspiring. So that’s it. Go watch the stars. Let your mind wander and wonder. Even if you don’t come away with any answers to the universe, at least you’ll have let your mind take a needed break, and that’s important too.

That’s it for this post and for our discussion on building your own solar system. Was there anything in this episode that surprised you? Soon we can start working on the geography of our worlds, so I will see you next time!

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